The present invention relates to the field of digital image processing, and more particularly to color calibration and color enhancement for digital imaging systems.
Continual advances in computer technology are making possible cost effective color digital imaging systems capable of displaying high resolution images. The proliferation of these imaging systems is driving a need for predictable color matching between the image scanner, the display, and the hard copy devices. In color digital imaging, each aspect of the imaging chain, including the lighting of the original scene as well as the capturing, storage, transmission, and display of the image on screen or hard copy devices, generally involves different color spaces in conjunction with different color gamuts. Most of the color spaces are device dependent. A color gamut is the range of colors which can be reproduced on a particular device. In this context, accurate descriptions of how various devices in a typical work flow represent color are required.
One method to ensure consistent color characteristics is to calibrate the color display and hard copy devices to particular set up parameters. A description of a device with respect to the way it represents color is stored in a"profile" of that device. Based on the type of the device, certain parameters are required in order to completely and accurately characterize the device.
For example, in the case of display devices, these parameters include the X, Y, and Z coordinates of the media white point; the relative X, Y, Z values corresponding to red, green and blue; and the red, green and blue tone reproduction curves. The XYZ values are the three standard primary colors of the CIE chromaticity diagram. Once all devices involved in a particular work flow are appropriately characterized by the corresponding profiles, color management systems can be used to convert colors from the color space of one device to the color space of another device, therefore leading to consistent color reproduction across the devices as well as operating system platforms.
Several products are currently available for accurately measuring the characteristics of various display and hard copy devices. With the aid of such tools, the user can display an image having known color characteristics and manually calibrate the display screen to produce known characteristics of the image on a display screen or on a hard copy device. However, since most computer users do not have access to relatively expensive measurement and calibration equipment, these users generally resort to an alternate solution of using a software tool in conjunction with a physical template whose brightness and hue are compared and matched to that of the display. However, the use of the matching template is not optimal as the screen and the template are made from different media (emissive versus reflective). Additionally, software tools in this category require that a template be readily available for comparison purposes.